A sensitive 1 H NMR spectroscopic method for the quantification of capsaicin and capsaicinoid: morpho-chemical characterisation of chili land races from northeast India.

Abstract

Proton (1 H) nuclear magnetic resonance (NMR) spectroscopy based analytical method for the quantification of capsaicin (major pungent principle of chili) has certain advantages including short data acquisition time and better structural authentication. Earlier NMR methods are associated with either of the bottlenecks such as low or lack of information on the sensitivity and scope for the quantification of total capsaicinoid. To develop a sensitive 1 H quantitative NMR (qNMR) technique for capsaicin and total capsaicinoid in dry chili and chili oleoresin and to demonstrate its applicability in a real sample set. A 1 H qNMR method was developed using benzene as the internal standard for the quantification of capsaicin (terminal methyl signal) as well as total capsaicinoid (benzyl methylene signal) in dry chili and oleoresin and validated in terms of specificity, linearity, sensitivity, accuracy and precision. The developed 1 H qNMR method was specific, sensitive (limit of detection 4.4 μg/mL and limit of quantitation 14.8 μg/mL), linear in the range 0.083-8.33 mg/mL of capsaicin, accurate and precise. The credibility of the developed method was showcased in the morpho-chemical characterisation of commercially available 15 chili land races from northeast India. The analysis identified the land races with a wide range of capsaicin (trace to 1.49% in the dry fruit and trace to 6.21% in the oleoresin w/w) and oleoresin content (3.35-26.78% w/w). The standardized 1 H qNMR method facilitated the findings of chemical basis for the selection of chili land races from this region, capable of producing high-yielding oleoresin with intended degree of pungency.